Incandescent electric lamp with etalon type transparent heat mirror

Claim 1

An incandescent electric lamp comprising a sealed envelope of a material which is transparent to light in the visible range, an incandescent filament within said envelope, means for supplying electrical current to said filament to cause it to incandesce at a temperature so as to produce light energy in at least a portion of the visible range and energy in the infrared range, the major portion of said envelope being optically shaped with a curved surface curved in at least two directions in any given area to reflect energy back toward and to impinge upon said filament, an etalon coating located directly on a substantial part of the curved surface portion of the envelope, said coating comprising only a single triad of films consisting of a film of a dielectric material sandwiched between and in direct contact with two films of an electrically conductive metal with one of said films of electrically conductive metal being deposited directly on the envelope, said films being matched to the characteristics of both the visible range light energy and the infrared range energy produced by the filament for transmitting exterior to the lamp at least about 80% of the visible range light energy at the peak of the luminosity curve of the visible range light energy produced by the filament and for reflecting at least about 75% of the energy in the infrared range at about 1.0 micron and above back towards the filament to impinge thereon to thereby increase the operating temperature of the filament and to reduce the amount of electrical current needed to heat said filament to incandescence.